1556 - Calculating Area

Time Limit: 1s Memory Limit: 128MB

Submissions: 186 Solved: 55
Description
       This problem is very straightforward, in a 2-D plane, Give you a polygen, you need calculate its area.
Input
       One integer T indicates the number of test cases
       Each case is started with one integer n which means the number of points of that polygen then n lines followed, each line is a pair of real number x y describe the x-coordinate and y-coordinate of point, points are descriped counter clockwise.
Output
       One real number rounded up to 2 decimal indicates the area of polygen.
Sample Input
2
4
0 0
1 0
1 1
0 1
3
0 0
1 0
1 1
Sample Output
1.00
0.50
Hint
 
Source
The 6th ACM Programming Contest of HUST